1. Field of the Invention
This invention relates to various improvements to the methods and apparatus disclosed in U.S. Patent Publication Nos. 2009/0062782 and 2009/0149845, and other similar laser treatment methods and apparatus involving monitoring of the treatment site for conditions such as overheating. The improvements include:    a. Addition of a variable time delay control to allow a surgeon to delay interruption of laser firing upon detection of overheating;    b. Addition of a detector sensitivity control for changing a sensitivity of the detector.The invention may take the form of a hand held controller with an LCD or equivalent display and buttons or other inputs for setting the power output of the laser, the time delay, numerical aperture of the laser, and the sensitivity of the feedback detector.
The above listed improvements may be used separately or in any combination with each other or with any elements of the system disclosed in U.S. Patent Publication Nos. 2009/0062782 and 2009/0149845, or in combination with other surgical laser methods and systems, including those described in U.S. Patent Publication Nos. 2009/0062782 and 2009/0149845 as prior or related art. The methods and apparatus of the invention may be used with a variety of surgical laser procedures, including vascular surgery, liposuction, and applications involving gastroenterology, oncology, and urology.
2. Description of Related Art
A number of copending patent applications, prior patents, and prior publications, address the problem of detecting and preventing damage due to overheating of tissues and/or instruments/devices used to deliver laser energy to tissues during laser surgery or therapeutic laser procedures. For example, U.S. Patent Publication No. 2009/0062782 (based on U.S. patent application Ser. No. 12/047,819) discloses a safety feedback control unit in which radiation resulting from overheating at the location of the surgery is detected and used to control fiber position, laser activation, or rate of pullback. U.S. Patent Publication No. 2009/0149845 (based on U.S. patent application Ser. No. 12/073,922) discloses a radiation feedback system in which a sensor at the treatment end of the fiber monitors wavelengths indicative of temperature at the treatment end so that overheating of tissues can be detected before the flash of light from pyrolytic burning occurs, and monitoring of the output of the laser by downstream deflection, absorption, or fiber movement in response to overheating detection. In addition, various improvements on these safety or feedback systems are disclosed in PCT Publication PCT/US2009/006021. Each of these publications is incorporated herein by reference, and many the principles disclosed in U.S. Patent Publication Nos. 2009/0062782 and 2009/0149845, and PCT Publication No. PCT/US2009/006021, have been implemented in the LaserGuard™ system made by Optical Integrity, Inc. of Panama City, Fla.
The present invention is in response to various discoveries made by the inventor concerning the specific causes of damage and injury that occur during laser surgery. Conventionally, it was believed that damage caused by overheating during surgery was indicated by the pyrolytic glow that occurs during burning of tissues. As a result, various feedback systems were proposed to detect glowing of the tissues, and shut down of the laser upon detection of visible light from the glowing tissue. An example of such as system is disclosed in U.S. Pat. No. 5,098,427 (Hessel), owned by Messerschmitt-Bolkow-Blohm GmbH (MBB).
However, the inventor has discovered that glowing of tissues by itself does not necessarily indicate that damage or injury will occur. Instead, in many applications, the primary cause of fiber damage and resulting injury to the patient, namely fiber fusing or free electron absorption (FEA), normally occurs only when the fiber tip contacts the tissue during operation of the laser, which causes an increase in the temperature at the fiber tip. When the temperature at the fiber tip exceeds 1000 C, fiber fusing or FEA occurs, creating temperatures higher than 5000 C, at which point fiber fusing or FEA results in damage to the fiber.
There are several consequences of this discovery. First, it is not necessary to shut down the laser right away each time a glow is detected during surgery. Instead, it may be enough to simply move the tip of the laser away from the tissue and continue operating the laser, or to continue the procedure until the intensity of the glow or detected temperature exceeds a certain threshold. Second, the amount of energy that the laser can safely deliver to the patient without risk of injury may be higher than previously believed. These consequences suggest that certain laser procedures may be accomplished in a shorter time, without as many interruptions, thereby reducing discomfort to the patient. On the other hand, higher laser power can mean greater pain, and thus for certain applications, it might be desired to try and reduce the amount of laser energy delivered to the patient. The present invention seeks to take into account the inventor's discoveries concerning the specific causes of fiber damage and injury during laser surgery.